Previous estimates of mortality in Iraq attributable to the 2003 invasion have been heterogeneous and controversial, and none were produced after 2006. The purpose of this research was to estimate direct and indirect deaths attributable to the war in Iraq between 2003 and 2011.

Methods and Findings

We conducted a survey of 2,000 randomly selected households throughout Iraq, using a two-stage cluster sampling method to ensure the sample of households was nationally representative. We asked every household head about births and deaths since 2001, and all household adults about mortality among their siblings. We used secondary data sources to correct for out-migration. From March 1, 2003, to June 30, 2011, the crude death rate in Iraq was 4.55 per 1,000 person-years (95% uncertainty interval 3.74–5.27), more than 0.5 times higher than the death rate during the 26-mo period preceding the war, resulting in approximately 405,000 (95% uncertainty interval 48,000–751,000) excess deaths attributable to the conflict. Among adults, the risk of death rose 0.7 times higher for women and 2.9 times higher for men between the pre-war period (January 1, 2001, to February 28, 2003) and the peak of the war (2005–2006). We estimate that more than 60% of excess deaths were directly attributable to violence, with the rest associated with the collapse of infrastructure and other indirect, but war-related, causes. We used secondary sources to estimate rates of death among emigrants. Those estimates suggest we missed at least 55,000 deaths that would have been reported by households had the households remained behind in Iraq, but which instead had migrated away. Only 24 households refused to participate in the study. An additional five households were not interviewed because of hostile or threatening behavior, for a 98.55% response rate. The reliance on outdated census data and the long recall period required of participants are limitations of our study.

Conclusions

Beyond expected rates, most mortality increases in Iraq can be attributed to direct violence, but about a third are attributable to indirect causes (such as from failures of health, sanitation, transportation, communication, and other systems). Approximately a half million deaths in Iraq could be attributable to the war.

Please see later in the article for the Editors' Summary

Editors' Summary

Background

War is a major public health problem. Its health effects include violent deaths among soldiers and civilians as well as indirect increases in mortality and morbidity caused by conflict. Unlike those of other causes of death and disability, however, the consequences of war on population health are rarely studied scientifically. In conflict situations, deaths and diseases are not reliably measured and recorded, and estimating the proportion caused, directly or indirectly, by a war or conflict is challenging. Population-based mortality survey methods—asking representative survivors about deaths they know about—were developed by public health researchers to estimate death rates. By comparing death rate estimates for periods before and during a conflict, researchers can derive the number of excess deaths that are attributable to the conflict.

Why Was This Study Done?

A number of earlier studies have estimated the death toll in Iraq since the beginning of the war in March 2003. The previous studies covered different periods from 2003 to 2006 and derived different rates of overall deaths and excess deaths attributable to the war and conflict. All of them have been controversial, and their methodologies have been criticized. For this study, based on a population-based mortality survey, the researchers modified and improved their methodology in response to critiques of earlier surveys. The study covers the period from the beginning of the war in March 2003 until June 2011, including a period of high violence from 2006 to 2008. It provides population-based estimates for excess deaths in the years after 2006 and covers most of the period of the war and subsequent occupation.

What Did the Researchers Do and Find?

Interviewers trained by the researchers conducted the survey between May 2011 and July 2011 and collected data from 2,000 randomly selected households in 100 geographical clusters, distributed across Iraq's 18 governorates. The interviewers asked the head of each household about deaths among household members from 2001 to the time of the interview, including a pre-war period from January 2001 to March 2003 and the period of the war and occupation. They also asked all adults in the household about deaths among their siblings during the same period. From the first set of data, the researchers calculated the crude death rates (i.e., the number of deaths during a year per 1,000 individuals) before and during the war. They found the wartime crude death rate in Iraq to be 4.55 per 1,000, more than 50% higher than the death rate of 2.89 during the two-year period preceding the war. By multiplying those rates by the annual Iraq population, the authors estimate the total excess Iraqi deaths attributable to the war through mid-2011 to be about 405,000. The researchers also estimated that an additional 56,000 deaths were not counted due to migration. Including this number, their final estimate is that approximately half a million people died in Iraq as a result of the war and subsequent occupation from March 2003 to June 2011.

The risk of death at the peak of the conflict in 2006 almost tripled for men and rose by 70% for women. Respondents attributed 20% of household deaths to war-related violence. Violent deaths were attributed primarily to coalition forces (35%) and militia (32%). The majority (63%) of violent deaths were from gunshots. Twelve percent were attributed to car bombs. Based on the responses from adults in the surveyed households who reported on the alive-or-dead status of their siblings, the researchers estimated the total number of deaths among adults aged 15–60 years, from March 2003 to June 2011, to be approximately 376,000; 184,000 of these deaths were attributed to the conflict, and of those, the authors estimate that 132,000 were caused directly by war-related violence.

What Do These Findings Mean?

These findings provide the most up-to-date estimates of the death toll of the Iraq war and subsequent conflict. However, given the difficult circumstances, the estimates are associated with substantial uncertainties. The researchers extrapolated from a small representative sample of households to estimate Iraq's national death toll. In addition, respondents were asked to recall events that occurred up to ten years prior, which can lead to inaccuracies. The researchers also had to rely on outdated census data (the last complete population census in Iraq dates back to 1987) for their overall population figures. Thus, to accompany their estimate of 460,000 excess deaths from March 2003 to mid-2011, the authors used statistical methods to determine the likely range of the true estimate. Based on the statistical methods, the researchers are 95% confident that the true number of excess deaths lies between 48,000 and 751,000—a large range. More than two years past the end of the period covered in this study, the conflict in Iraq is far from over and continues to cost lives at alarming rates. As discussed in an accompanying Perspective by Salman Rawaf, violence and lawlessness continue to the present day. In addition, post-war Iraq has limited capacity to re-establish and maintain its battered public health and safety infrastructure.

Funding: Support for this study came from pooled internal resources by the American and Canadian researchers without external funding. No funding bodies had any role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.